Google will no longer let other services automatically import its users' email contact data for their own purposes, unless the information flows both ways. It accused Facebook in particular of siphoning up Google contact data, without allowing for the automatic import and export of Facebook users' information.

Google said that while it makes it easy for other Web services to automatically import a user's contact data, Facebook was not reciprocating.

"We have decided to change our approach slightly to reflect the fact that users often aren't aware that once they have imported their contacts into sites like Facebook, they are effectively trapped," Google said in an emailed statement.

"We will no longer allow websites to automate the import of users' Google Contacts (via our API) unless they allow similar export to other sites," Google said.